ATMOPACS Streszczenie raportu

In the past 20 years ambient air pollution, most notably particulate matter (PM), has come to be recognized as a risk factor contributing to declines in respiratory and cardiovascular health and increased risk of acute morbidity and mortality from all non-accidental causes. It has been estimated that a reduction of the ambient concentration of particles by 5 micrograms per cubic metre in Europe can “prevent” between 3000 and 8000 early deaths annually. At the same time, atmospheric aerosol particles influence the Earth's radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei (CCN). The role of these particles in the energy balance of our planet is one of the major uncertainties in the global change problem.

Organic compounds are important components of atmospheric sub-micrometer particles constituting roughly half of their mass. However, while the inorganic fraction of fine PM is relatively well understood, significant uncertainty clouds our understanding of almost all aspects of organic particulate matter, including its sources, atmospheric transformation, and fate. Organic aerosol has been viewed as a relatively inert, non-volatile mixture of compounds from a complex array of primary sources (primary organic aerosol), coated by secondary compounds derived from gas-phase oxidation of volatile precursors (secondary organic aerosol). The chemical complexity of the OA (there are thousands or even ten of thousands of complex large organic compounds in typical ambient aerosol), its unknown chemical composition (less than 20% of the OA mass has been quantified even by the best studies), the unknown physical and chemical properties of the majority of the known OA components, and the difficulty of describing mathematically such a complex system in atmospheric chemical transport models (CTMs) have seriously limited scientific progress in both the air quality and climate change areas. CTMs in both regional and global scales are in general not able to reproduce the observed OA levels, their chemical characteristics (degree of oxidation), their diurnal variation, etc. As a result, it has not been possible to evaluate the effects of different strategies of reduction of OA concentrations in polluted areas and to quantify the effect of OA on the energy balance of the planet.

In ATMOPACS we have developed a new framework to reduce the complexity of the atmospheric OA to just two of its properties: volatility and oxygen to carbon. So instead of trying to measure and simulate the tens of thousands of organic compounds in our atmosphere, we focus on the distribution of OA as a function of these two variables. We have shown that it is possible to describe the average composition of the OA, its thermodynamics and evolution in this framework and developed a new naming system for the OA components to facilitate interactions among scientists and with the decision makers. We have continued the development of measurement techniques for the volatility distribution and oxygen content distribution of OA that allow the experimental characterization of OA in this new “coordinate system”. A combination of gently heating the particles and in parallel diluting them isothermally, while monitoring continuously their chemical composition with an Aerosol Mass Spectrometer and their size with a Scanning Mobility Particle Sizer, was shown to be the best measurement approach.These measurement techniques have been tested in ambient measurements in Europe.

The most surprising result was the unexpected dominance of wood burning combustion as a source of organic aerosol. Sources included burning of agricultural waste (olive trees for the Mediterranean countries), wildfires, and domestic wood burning for heating processes. We showed that while these particles are quite different these beginning depending on the fuel burned and the conditions of the burning, the age chemically in the atmosphere. This aging is rapid (it takes place in a day) and converts the particles to highly oxygenated particulate matter that can act as condensation nuclei for the formation of clouds. The resulting OA disperses over large distances away from its sources becoming part of the background OA in Europe.

We have incorporated our findings in a three-dimensional chemical transport model that simulates air quality over Europe. The comparison of its predictions for the OA concentration levels and oxygen content in different parts of Europe were encouraging and represent an improvement compared to the existing models. The model suggests that most of the OA even in major urban areas in Europe is on average the result of emissions away from the city and is quite oxygenated in the summer. This secondary OA can have a significant impact on the radiative balance of Europe. Controls of ammonia emissions, sulphur dioxide, and primary organic emissions are promising strategies for the reduction of particulate matter levels over Europe and the corresponding improvement of human health.